Queues & messaging Study Portal

Key takeaways

• Work queue for jobs, pub/sub for fan-out events, partitioned log for replayable ordered streams.
• At-least-once plus idempotent consumers is the practical guarantee; exactly-once is effectively-once.
• Outbox for publishing, inbox or dedup table for consuming: no distributed transaction needed.
• Order per key by partitioning on that key; retries can reorder.
• Exponential backoff with jitter for transient errors, DLQ for permanent ones, and someone who owns the DLQ.
• Monitor consumer lag in seconds; queues absorb bursts but do not add capacity.